Tennis rackets and frames therefor

ABSTRACT

The invention concerns tennis rackets whose frames are formed from steel tube (so called &#39;&#39;&#39;&#39;steel tennis rackets&#39;&#39;&#39;&#39;) of enhanced rigidity which gives them superior playing properties. This rigidity can be obtained by choosing steel tube whose dimensions are as follows: (A) the maximum external dimension of the tube cross-section divided by the maximum wall thickness of the tube at the cross-section is at least 26; and (B) the minimum external dimension of the tube cross-section divided by the maximum wall thickness of the tube at the cross-section is at least 13. If the tube is of oval cross-section, the maximum external dimension of the cross-section is preferably in a direction transverse to the plane containing the racket frame, of which the following is a specification.

llmted States Patent 1191 1111 mohaoz lllaines et a1. [45] M 7, 1974TENNIS RACKETS AND FRAMES 3,086,777 4/1963 Lacoste 273/73 1-1 THEREFOR3,431,626 3/1969 Carlton 273/73 H 3,582,073 6/1971 Melnick et al 273/73H [75] Inventors: Robert C. Haines, Huddersfield;

John E. Barre, FOREIGN PATENTS OR APPLICATIONS Kingston on-Thames; EricH, l6,9l4 7/l9l I Great Britain 273/73 H Stevens, Monk Bretton a of346,001 4/1931 Great Britain 273/73 H England 8,112 5/1884 Great Britain273/73 H I Assigneei Dunlop Holdings, Limlled, Primary Examiner-RichardC. Pinkham James London England Assistant Examiner-Richard J. Apley [22]Filed: Sept 5, 1972 Attorney, Agent, or Firm-Stevens, Davis, Miller andMosher [21] Appl. No.: 286,001

Related US. Application Data ABSTRACT [63] continuatiommpan f s 39 Dec,3 The invention concerns tennis rackets whose frames 1969, abandoned areformed from steel tube (so called steel tennis rackets") of enhancedrigidity which gives them supe- [30] Foreign Application Priority Datarior playing properties. This rigidity can be obtained Jan 30 1969 GreatBritain h 367/69 by choosing steel tube whose dimensions are as follows:(A) the maximum external dimension of the 52 us. on. 273/73 (3, 273/73 Htube Cross-Section divided y the maximum Wall thick- 51 11m. (:1 A63b49/12 Hess Of the tube at the Cross-section is at least 26; and [58]Field f searchm 2 3 73 R, 7 C, 7 D, 7 G, (B) the minimum externaldimension of the tube 273/73 H cross-section divided by the maximum wallthickness of the tube at the cross-section is at least 13. If the 5References Cited tube is of oval cross-section, the maximum externalUNITED STATES PATENTS dimension of the cross-section is preferably in adirection transverse to the plane containing the racket its? 273/73 Hframe, of which the following is a specification. 2,171,223 8/1939Robinson 273/73 H 12 Claims, 11 Drawing Figures TEST NO. 3

P-METEW m4 3309.402 SHEET 2 HF A FIG] WT. MAX. WALL THICKNESS L MIN.EXT. DIA.

R H "l3 ELATIONS IP B W MAX. WALL THICKNESS PATENTEDMAY 71914 9402 I Isumuura TEST NO. 4

ll TENNIS RACKETS AND FRAMES THEREFOR This application is acontinuation-in-part of our copending application Ser. No. 889,642 filedDec. 31, I969 and now abandoned.

This invention relates to steel tennis racket frames and rackets madefrom them.

To illustrate this invention attention is directed to the attacheddrawings in which:

FIG. l is a plan view of a thin shaft tennis racket showing itsprincipal parts;

FIG. 2 is a plan view of a tennis racket showing the location of testsperformed thereon;

FIGS. 3 to 7 illustrate cross-sections of steel tubes used for frames ofrackets of this invention;

FIGS. 8 to 11 illustrate the positioning and apparatus for a tennisracket while conducting distortion tests I to 4, respectively.

DESCRIPTION OF THE INVENTION During recent years considerable work hasbeen done in the development of tennis rackets having steel frames,usually referred to simply as steel tennis rackets." These rackets are,for example, often in the form shown in FIG. I of the accompanyingdrawings, in which the head (A) and the twin shafts (B) are made from alength of hollow steel tube, and the frame is completed by means ofabridge-piece (C) and a brace (D) which may or may not be made from thesame type of tubing as used for the head and shafts. Hitherto, it hasbeen believed that flexibility in the racket frame was a desirablefeature, and indeed whippy" shafts have been acclaimed as an advantageof steel rackets over wooden rackets.

We have now found that conventional steel rackets are in fact notsufficiently rigid and that considerable improvement is obtained byusing frames of increased rigidity. Our experiments have shown thatduring contact with a ball the conventional racket is distorted,particularly by bending along the longitudinal axis X-X (FIG. 1), and/orby twisting about this axis when the ball strikes the racketasymmetrically. Distortion of the racket in this way results in areduced amount of energy being imparted to the ball by the racketbecause the strings are not caused to be elastically distorted to thesame degree as would occur if the frame were more rigid. Moreover, insome instances the player experiences difficulty in hitting the ballaccurately in the intended direction because the direction of flight ofthe ball on leaving the racket is effected by the angular distortion ofthe head of the racket.

However, recognition by us of these deficiencies of conventional steelrackets did not lead to a ready solution. To a large extent thedifficulty lay in the need to retain the desirable playing qualities ofthe rackets and to avoid increasing the weight of the racket beyond whatis acceptable by the players. It was also necessary, from a commercialaspect, that the racket should have an attractive appearance which willappeal to players, and this factor alone obviated several solutions tothe problem which might otherwise have been possible.

We have now found according to the present invention that rackets of thenecessary rigidity can be obtained by the use for the frame of steeltube having a particular cross-section. Thus, we have found that thedimensions ofa cross-section of the tube at right-angles to itslongitudinal axis should be such that:

a. The ratio of the maximum external dimension of the tube cross-sectionthroughout the frame on the axis perpendicular to the plane containingthe racket frame (i.e., the major axis of the cross-section) to themaximum wall thickness of the tube at said cross-section (RelationshipA) is at least 26, and I b. The ratio of the external dimension of thetube cross-section throughout the frame on the axis perpendicular to andpassing through the midpoint of said major axis (i.e., the minor axis ofthe cross-section) divided by the maximum wall thickness of the tube atsaid cross-section (Relationship B) is at least 13. Relationship A ispreferably in the range 26 to 52 and especially in the range 30 to 42;and Relationship B is preferably in the range 13 to 28 and especially inthe range 20 to 28.

By way of example, the racket frames of this invention are describedhereinafter with reference to the use of twin shafts such as that shownin FIG. 1 of the accompanying drawings, but the invention is not limitedto the use of twin shafts and, for example, a single shaft can be used.

A further aspect of the present invention is based on the discovery thata steel racket, if it is to be ofa desirable rigidity, should preferablyhave one or more of the following special characteristics as measured byphysical tests described below with reference to FIG. 2 of the drawingsand referred to respectively as distortion tests I, 2, 3 and 4. Thesetests are illustrated in FIGS. 8-11 respectively. All four tests aremade on the frame, that is the racket before stringing; and tests 1,2'and 3 should be made after the grip has been affixed to the frame.Test 4 may also, if desired, be made after the grip has been affixed tothe frame.

DISTORTION TEST 1 DEFLECTION OF HEAD WITH HANDLE CLAMPED (SEE FIG. 8).

The last 6 inches of the handle end of the frame is clamped firmly withthe strings in a horizontal position.

Using a bridge attachment 12 a load W of 50 lbs is applied to the centerof the head of the frame at a point L 14 inches from the edge of theclamp (i.e., 20 inches from the grip end) so that the head is deflecteddownwardly in a vertical direction. The displacement d of the head, overlength P, at the point H-is then measured.

DISTORTION TEST 2 TWIST OF HEAD WITH HANDLE CLAMPED (SEE FIG. 9).

The frame is clamped as in Test 1 and the head is twisted about thelongitudinal axis of the handle but with no linear displacement. Thetwisting couple T is applied on the line YZ by means ofa counterweighted beam 13 fastened to the head, 14 inches from the clamp edge.Loads are applied in opposite directions at positions Y and Z in thedirection shown by the arrows to provide a torque of inch pound, and theangular displacement at of the frame is measured at line YZ. The testmeasures torsional stiffness of the frame be tween the clamps.

DISTORTION TEST 3 DEFLECTION OF HANDLE WITH HEAD CLAMPED (SEE FIG. 10).

The crown of the racket up to line PG (6 inches from H) is clampedfirmly in a horizontalposition. A load W of 20 lbs is applied at the endE of the handle and the DISTORTION TEST 4 DISTORTION OF HEAD IN PLANE OFSTRINGS (SEE FIG. 11).

The frame without strings is gripped between hooked jaws l4 and in atension testing machine at l and .l.

A load is steadily applied to the frame in a direction opposed to thedirection of tension normally exerted by the transverse strings. Thedeflection X of the frame under the steadily increasing load is plottedin the form of a graph, and the load deflection ratio at a deflectionvalue of one-tenth of an inch is calculated as load (lb)/deflection(inch).

According to a further aspect of the invention, steel rackets preferablyhave the following properties as measured by the distortion tests:

1. Distortion Test 1.

The vertical displacement of H is not more than 1% inches, preferablynot more than 1% or 1 /2 inches.

2. Distortion Test 2.

Under a torque of 150 inch pound the angular distortion of the head isnot more than 4, preferably not more than 3.

3. Distortion Test 3.

The. vertical displacement of E is not more than 1% inches, preferablynot more than 1% or 1 /2 inches.

4.,Distortion Test 4.

The load deflection ratio is greater than 450.

The invention is illustrated in the following examples with reference tothe accompanying drawings. In the drawings'FlG. I is a plan view ofatennis racket whose head A and twin shafts B are constituted by a singlelength of drawn steel tube whose cross-section is uniform along itswhole length; FIG. 2 is a diagrammatic representation of a racket of theinvention to illustrate the various distortion tests; and FIGS. 3 to 7are respectively cross-sections of steel tubes used for the framesEXAMPLES Examples 1 to 4 refer respectively to four steel tennis racketsconstructed in the form shown in FIG. 1 and having a cross-section atright-angles to the longitudinal axis of the tube, (for example on theline X-X) as shown respectively in FIGS. 3 to 6. Thus, for example, thecross-section of the tube of Example 1 (FIG. 3) is circular whereas thatof Example 2 (FIG. 4) is oval.

The racket of Example I, being constructed ofa steel tube of circularcross-section has the same values for maximum and minimum (i.e., majorand minor axes respectively) external dimensions, in each case being0.625 inch. The wall thickness is 0.023 inch. Thus, both relationships Aand B are obtained by the expression: 0.625/0.023 27.2

In Example 2 (see FIG. 4), where the tube has an oval cross-section anda uniform wall thickness of 6 0.022 inch the relationships A and B areobtained as follows:

Relationship A Major axis external dimension/maximum wall thickness0.700/0.022 31.8 Relationship B Minor axis external dimension/maximumwall thickness In Example 3 (see FIG. 5), where the wall thickness is0.020 inch the major axis external dimension is 0.580 and the minor axisexternal dimension is 0.350 inch.

Thus Relationship A 0.580/0.020 29.0 Relationship B 0.350/0 .0 20 l 7.5

In Example 4 (FIG. 6) the cross-section of the tube is oval but in thisinstance the wall thickness varies between 0.025 inch and 0.010 inch.The major axis external dimension is 0.680 inch and the minor axisexternal dimension is 0.450 inch.

Thus Relationship A 0.680/0.025 27.2

Relationship B 0.4 50/0.025 18.0

EXAMPLE 5 There now follows, with reference to FIGS. 1 and 7 of theaccompanying drawings, a description of the manufacture of a tennisracket according to a preferred embodiment of the invention from alength of steel alloy tubing of oval cross-section. The major axis(external dimension) of the cross-section was 0.71 1 inch and the minoraxis (minimum external dimension) was 0.497 inch. The wall thickness ofthe tube was 0.018 inch. A length of this tube 5 feet 1 inch long wasfirst grooved along a length of 21 inches situated symmetrically in themiddle of the tube length. This groove was l/16 inch wide and 3/32 inchdeep. The tube was filled with a molten bitumen supporting materialwhich was allowed to solidify, and the tube was then bent into the shapeof a racket frame so that the groove in the tu he now lay along theouter edge of the loop of the frame (A-FIG. 1). A series of holes weredrilled in the loop, the edges of the holes then being deformed byindentation towards the interior of the tube to provide the stringingapertures. The bitumen support material was then melted and drained fromthe tube.

A bridge piece (C) having appropriate stringing apertures was preparedin a similar way to that described above and then brazed onto the frameloop to provide the head of the racket. Two braces (D) were brazedbetween the parallel ends (B) of the frame, the upper brace being insuch a position that when the wooden handle was subsequently applied,the top of the upper brace coincided with the top of the handle.

The frame was electroplated with chromium and nickel and then two, likewooden handle pieces were glued together about the handle end of theframe and then bound with leather to provide the handle. The racket wascompleted by the insertion of nylon grommets into the stringingapertures and then strung in a conventional manner.

The racket frame of Example 5, before stringing, was subjected todistortion test 1, 2, 3 and 4, and the following results were obtained:

Test 1: 1.1 inches deflection.

Test 2: 2% degrees angular distortion.

Test 3: 1.2 inches deflection.

Test 4: 580 load deflection ratio.

ing uniformly throughout the length of said frame.

2. A frame according to claim 1, in which Relationship A is in the range26 to'52.

3. A frame according to claim 1, in which Relationship B is in the range13 to 28.

4. A tennis racket frame according to claim 1, which when subjected todistortion test 3 (as hereinbefore defined) shows a verticaldisplacement of not morethan 1% inches.

5. A tennis racket frame according toclaim l, which when subjected todistortion test 1 (as hereinbefore de- Maximum Minimum Maximum ExternalExternal Wall Example Figure Dimension Dimension Thickness RelationshipRelationship B A No. No.

- (inch) (inch) (inch) (major axis) (minor axis) 1 3 0.625 0.625 0.02327.2 27.2 2 4 0.700 0.500 0.022 3 l .8 22.7 .1 5 0.580 0.350 01020 29.0[715 4 6 (L680 0.450 0.025 27.2 NH) 5 7 0.7ll 0.497 0.018 39.5 27.6

We claim:

1. A tennis racket frame of greater than conventional rigidity having ahead, a throat, a handle portion and a grip at the end of said handleportion, said frame com.- prising a steel tube having a uniform maximumwall thickness and a cross-section measured at right-angles to itslongitudinal axis such that,

a. the ratio of the maximum external dimension of the tube cross-sectionthroughout the frame on a first axis perpendicular to the planecontaining the racket frame (i.e., the major axis of the crosssection)to said maximum wall thickness of the tube at said cross-section(Relationship A) is at least 26, and

b. the ratio of the external dimension of the tube cross-sectionthroughout the frame on a second axis perpendicular to and passingthrough the midpoint of said first perpendicular axis (i.e., the minoraxis of the cross-section) to said maximum wall thickness of the tube atsaid cross-section (Relationship B) is at least 13,

and said frame when subjected to distortion test 3 (as hereinbeforedefined) shows a vertical displacement of not more than 1 inches, saidratios existfined) shows a vertical displacement 1% inches.

6. A tennis racket frame according to claim 1, which when subjected todistortion test 1 (as hereinbefore defined) shows a verticaldisplacement of not more than 1% inches.

7. A tennis racket frame according to claim 1, which when subjected todistortion test 2 (as hereinbefore defined) shows (under a torque ofinch pound) an angular distortion of not more than 4.

8. A tennis racket frame according to claim 1, which when subjected todistortion test 2 (as hereinbefore defined) shows (under a torque of 150inch pound) an angular distortion of not more than 3 degrees.

9. A tennis racket frame according to claim 1, which when subjected todistortion test 4 (as hereinbefore defined) shows a load deflectionratio greater than 450.

of not more than 10. A tennis racket frame according to claim 1, inwhich the tube is of circular cross-section.

l1. Atennis racket frame according to claim 1, in which the tube is ofoval cross-section.

12. A tennis racket obtained by stringing a frame as claimed in claim 1.

1. A tennis racket frame of greater than conventional rigidity having ahead, a throat, a handle portion and a grip at the end of said handleportion, said frame comPrising a steel tube having a uniform maximumwall thickness and a cross-section measured at right-angles to itslongitudinal axis such that, a. the ratio of the maximum externaldimension of the tube cross-section throughout the frame on a first axisperpendicular to the plane containing the racket frame (i.e., the majoraxis of the cross-section) to said maximum wall thickness of the tube atsaid cross-section (Relationship A) is at least 26, and b. the ratio ofthe external dimension of the tube cross-section throughout the frame ona second axis perpendicular to and passing through the midpoint of saidfirst perpendicular axis (i.e., the minor axis of the cross-section) tosaid maximum wall thickness of the tube at said cross-section(Relationship B) is at least 13, and said frame when subjected todistortion test 3 (as hereinbefore defined) shows a verticaldisplacement of not more than 1 3/4 inches, said ratios existinguniformly throughout the length of said frame.
 2. A frame according toclaim 1, in which Relationship A is in the range 26 to
 52. 3. A frameaccording to claim 1, in which Relationship B is in the range 13 to 28.4. A tennis racket frame according to claim 1, which when subjected todistortion test 3 (as hereinbefore defined) shows a verticaldisplacement of not more than 1 1/4 inches.
 5. A tennis racket frameaccording to claim 1, which when subjected to distortion test 1 (ashereinbefore defined) shows a vertical displacement of not more than 13/4 inches.
 6. A tennis racket frame according to claim 1, which whensubjected to distortion test 1 (as hereinbefore defined) shows avertical displacement of not more than 1 1/4 inches.
 7. A tennis racketframe according to claim 1, which when subjected to distortion test 2(as hereinbefore defined) shows (under a torque of 150 inch pound) anangular distortion of not more than 4*.
 8. A tennis racket frameaccording to claim 1, which when subjected to distortion test 2 (ashereinbefore defined) shows (under a torque of 150 inch pound) anangular distortion of not more than 3 degrees.
 9. A tennis racket frameaccording to claim 1, which when subjected to distortion test 4 (ashereinbefore defined) shows a load deflection ratio greater than 450.10. A tennis racket frame according to claim 1, in which the tube is ofcircular cross-section.
 11. A tennis racket frame according to claim 1,in which the tube is of oval cross-section.
 12. A tennis racket obtainedby stringing a frame as claimed in claim 1.